1. Field of the Invention
This invention relates to improvements in a vehicle turning behavior control system for obtaining a high vehicle front turning ability, and more particularly to such a vehicle turning behavior control system for a vehicle provided with an anti-skid braking system.
2. Description of the Prior Art
Hitherto a variety of vehicle turning behavior control systems have been proposed. One of them is disclosed, for example, in a Japanese Utility Model Provisional Publication No. 59-155264 in which a brake application timing for an outside wheel, with respect to a vehicle turning direction, is controlled to be retarded relative to a brake application timing for an inside wheel, thereby developing a difference in braking force between the inside and outside wheels. This provides an initial vehicle front turning ability to stabilize the turning of the vehicle. In addition, for the same purpose, it has also been proposed to positively decrease a braking force distribution to the outside wheel, with respect to the vehicle turning direction as compared with the inside wheel.
The above control methods can improve a vehicles front turning ability; however such a function to improve the turning ability is unavoidably impeded in the case of a vehicle provided with an anti-skid braking system. More specifically, in general, the anti-skid braking system is arranged to control brake hydraulic pressures for respective wheels in accordance with wheel speeds detected by wheel speed sensors. Thus, necessary braking forces are obtained and lateral forces without causing wheel lock-up which improves the braking performance of the vehicle.
However, in the case where the above-discussed control for improving the vehicle front turning ability is carried out in a vehicle provided with an anti-skid braking system, roll of the vehicle body and lateral load movement become greater, thereby quickening a slip increase of an inside wheel with respect to the vehicle turning direction during braking. As a result, an anti-skid braking control is applied to the inside wheel so that brake hydraulic pressure for the inside wheel is decreased. At this time, if the brake hydraulic pressure for the inside wheel is decreased as compared with that for the outside wheel, a setting mode of difference in braking forces between the inside and outside wheels is reversed relative to that required for improving the vehicle front turning ability. As a result, the vehicle front turning ability cannot be controlled under the anti-skid braking control in which brake hydraulic pressure control is made independently in left and right side wheels. Thus, it has been difficult to simultaneously effect both the vehicle front turning ability improving control and the anti-skid braking control. In view of this, it may be proposed to carry out a suitable braking force distribution to the brake hydraulic fluid (which has been reduced by the anti-skid braking control) for the inside wheel with respect to the vehicle turning direction, and further to prolong a pressure decreasing time of the brake hydraulic fluid for the outside wheel as compared with that for the inside wheel with respect to the vehicle turning direction. However, this results in braking force shortage.